A method for manufacturing a field emission includes: providing a CNT array; drawing a bundle of CNTs from the CNT array to form a CNT yarn; soaking the CNT yarn into an organic solvent, and shrinking the CNT yarn into a CNT string after the organic solvent volatilizing; applying a voltage between two opposite ends of the CNT string; bombarding a predetermined point of the CNT string by an electron emitter, until the CNT string snapping; and attaching the snapped CNT string to a conductive base, and achieving a field emission electron source. The field emission efficiency of the field emission electron source is high.